The present invention relates to a rotary electrode roll for resistance welding with a built-in liquid metal as a conductive medium which is used when the seam on the sides of the bodies of steel-made cans is subjected to electric resistance welding.
The welding step performed in accordance with the prior art will be explained with reference to FIG. 1.
First, can body blanks which have been cut into a given size are taken out from their stacking station 1 piece by piece to be formed into tubular bodies. The formed tubular bodies 2 are transferred to the right in the drawing with the overlapped portion on the side to be formed into a seam being at the top, so that the overlapped portion passes between an upper circular electrode roll 3 fixed to a shaft 6 fitted rotatably into a part of an upper arm 5 and rotating in the direction of the arrow a and a lower circular electrode roll 4 which has a rotary portion which can rotate freely around a fixed portion fixed at an end of a lower arm 7. The overlapped portion is heated by the electric resistance produced when it passes through the two electrodes, and the heated portion is pressed and welded.
Next, the lower circular electrode roll 4 used for the welding of the can bodies mentioned above is shown in FIG. 2.
FIG. 2 is a sectional view of the electrode roll 4 through the axis of rotation thereof, showing the fixed portion 8, and the 8 rotary portion 9 provided around the fixed portion 8 in a freely rotatable manner. The fixed portion 8 is a stepped tubular form comprising a disc portion 11 at the longitudinal center part of the shaft of said tubular form, and end portions 10 and 10' having a diameter smaller than that of the disc portion 11 and provided on the two respective side surfaces of said disc portion diameter, and a channel 13 is provided along the axis of the shaft; the two ends of channel 13 are sealed by blind patches 14 and 14'. Opening 15 and 15' for fixing pipes provided at the end portions 10 and 10' communicate with channel 13, and pipes (not shown) are fixed in the openings 15 and 15'.
The rotary portion 9 provided around the fixed portion 8 in a freely rotatable manner comprises a right member 16 and a left member 17, and the two members 16 and 17 are joined in an airtight manner with the aid of an airtight packing 18. Here, as is shown in the drawing, the two end portions of each of the left and right members are fitted around the end portions 10 and 10' of the fixed portion 8 having a smaller diameter in a freely rotatable manner through ball bearings 19 and 19'.
Rotary portion 9 has inner surfaces 25, 25' and 26 facing the two outer side surfaces 12 and 12' and the peripheral surface 20 of the disc portion 11 of the fixed portion 8 being, and gaps 27, 27' and 28 being almost equal to each other in width are formed between the rotary portion 9 and the disc portion 11. A conductive liquid metal is received in gaps 27, 27' and 28 to such an extent that said gaps are filled with the liquid metal almost entirely. A bolt pore 29 extends from the surface of the right member 16 to the gaps for injecting the conductive liquid metal into the gaps.
Further, in order to use pure gallium and other readily melting gallium metals such as binary metals including gallium/indium and gallium/tin as the conductive liquid metal for use in the electrode roll, metal rings 22 and 22' made of a hard metal, which function as isolation parts 24 and 24' for isolating said gaps from the outside of the electrode roll, are provided to the rotary portion 9 through elastic rings 21 and 21' positioned in the respective spaces between gaps 27 and 27' and the ball bearings 19 and 19'; metal rings 22 and 22' are constructed in such a manner that along the whole periphery they are slidably in contact with fixed metal rings 23 and 23' made of a hard metal fitted over the base of the disc portion 11 of the fixed portion 8. Lubricating oil is provided in the neighborhood of said sliding portion.
In addition, as a means for preventing the oxidation of the readily melting gallium metal, the interior of the gaps 27, 27' and 28 is filled with pressurized nitrogen gas after said readily melting metal is received in the gaps.
The above-mentioned readily melting metal consisting mainly of gallium is extremely easy to oxidize, and its oxide lowers the conductive function of the readily melting metal. Therefore, the isolation parts 24 and 24' mentioned above are provided as a means for preventing of oxidation. But, nevertheless, it has been known that the oxidation progresses, though gradually, by the contact with the oil for lubricating the isolation parts, thereby shortening the life span of the readily melting metal used as a conductive medium.